I received two copies of the common Treasure Shiny Baubles a moment ago. Except one of them wasn't. It was the common Arcane Item Clattering Bauble. Same graphic, same rarity (so there was no "Uncommon" pop-up or whatever to distinguish them). One day, when you implement the "loot all" button, players won't realize what they've looted.

I'm guessing you are unfamiliar with the history of the problem. Wolfenstein 3D and Doom got away with it because no one had any idea there was an issue. Then the Red Cross started noticing. Look at the history of Worms and you'll see: one version explicitly says "red cross" in descriptive text (not to mention the images), and the next magically changes everything to "green cross." And that, of course, is just a handful of games: keep looking, you'll see more.